How high do you rev this engine?
We use 7/16 Smith Bros. and Comp "tapered" pushrods in Dirty Bird/Goateus Maximus. 9,200 RPM, zero issues 3 years. 1/2" is massive overkill and VERY difficult to get into the limited room. 3/8 are fine for up to 250 @ the seat, so you should be "close" there.
Setting the E-head up in a vertical mill, using a long "end mill", one can enlarge the pushrod tubes "side side" without going "back/forth", avoiding the runner. About a 75-80 degree angle does the trick, laying the hole back toward the stud.
Jim
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